1. Field of the Invention
The present invention relates to a method of fabricating a liquid crystal display device, and more particularly, to a method of fabricating a liquid crystal display device by liquid crystal dropping or vacuum injection using a UV-hardening and thermo-hardening sealant.
2. Discussion of the Related Art
In response to an increasing demand for various types of displays devices, flat panel type displays such as liquid crystal display (LCD), plasma display panel (PDP), electro-luminescent display (ELD), and vacuum fluorescent display (VFD) have been developed. In particular, LCD devices have been commonly used because of their high resolution, light weight, thin profile, and low power consumption. In addition, LCD devices have been implemented in mobile devices such as monitors for notebook computers, and for monitors of computers and televisions. Accordingly, efforts to improve image quality of LCD devices contrast with benefits of their high resolution, light weight, thin profile, and low power consumption. In order to incorporate LCD devices as a general  image display, image qualities such as sharpness, brightness, and large-sized area, for example, must be maintained.
FIG. 1 is a plane view of a liquid crystal display device having a C/F substrate bonded onto a TFT substrate according to the related art. In FIG. 1, a thermo-hardening sealant is used to bond a second substrate (i.e., color filter (C/F) substrate) 150 on top of a first substrate (i.e., thin film transistor (TFT) substrate) 100 by conventional hot-press equipment. Although a single bonded glass panel is shown in FIG. 1, a plurality of glass panels are simultaneously bonded, the thermo-hardening sealant 110 is hardened, and the panels are cut into a plurality of individual unit panels. Then, liquid crystal material is injected into each of the unit panels by a vacuum injection process.
FIGS. 2A to 2D are cross-sectional views of a fabrication process of the liquid crystal display device along I-I′ of FIG. 1 according to the related art. In FIG. 2A, a first alignment layer 101 is formed on a first substrate 100, where an active area 120 is defined. Although not shown, the first substrate includes a thin film transistor array having a plurality of gate lines, data lines, pixel electrodes, and thin film transistors formed in the active area 120. In addition, metal patterns 140 are formed along one peripheral side of the active area 120 to function as a common line.
A second alignment layer 151 is formed on a second substrate 150. Although not shown, the second substrate 150 includes a black matrix, a plurality of color filter layers, and a common electrode formed in the active area 120. In addition, a black matrix layer 130 is formed on a periphery of the active area 120.
In FIG. 2B, spacers 102 are positioned on the first alignment layer 101, and a thermo-hardening sealant 110 is formed on the second alignment layer 151 along the periphery of the active area 120. The thermo-hardening sealant 110 is formed as a wide bead along the periphery of the active area 120 when a line width of the black matrix layer 130 is relatively large.
In FIG. 2C, the second substrate 150 is aligned over the first substrate 100 so that a surface of the second substrate 150 on which the thermo-hardening sealant 110 is formed faces downward. The first and second substrates 100 and 150 are then bonded to each other, and the thermo-hardening sealant 110 is hardened for one hour at 140° C. in a conventional hot press 170.
In FIG. 2D, after a cutting process is performed to create individual unit panels (not shown), a liquid crystal material 103a is injected into each of the unit panels through an injection inlet 111 (in FIG. 1) using a vacuum injection method. The liquid crystal material injection is performed by vacuum injection using a pressure difference between an interior of the unit panel at an ambient pressure of the processing chamber. The injection inlet for the liquid crystal material injection is sealed after completion of the liquid crystal injection process.
FIG. 3 is a plane view of another liquid crystal display device having a TFT substrate bonded onto a C/F substrate according to the related art. In FIG. 3, spacers (not shown) are positioned on a second substrate 150 having a color filter array formed in an active area 120 and a black matrix layer (not shown) is formed along a periphery of the active area 120. In addition, a thermo-hardening sealant 110 is formed on a portion of a metal pattern 140 outside the active area 120 of a first substrate 100 having a thin film transistor array formed in the active area 120 and the metal pattern 140 at one side of the periphery of the active area 120. The first and second substrates 100 and 150 are then bonded to each other so that the thermo-hardening sealant 110 faces a lower direction, and the thermo-hardening sealant 110 is thermo-hardened in a hot press. Accordingly, the thermo-hardening sealant 110 is formed thereon so as to have an injection inlet for injecting liquid crystals.
FIGS. 4A to 4D are cross-sectional views of a fabrication process of the along II-II′ of FIG. 3 according to the related art. In FIG. 4A, a first alignment layer 101 is formed on a first substrate 100 having a thin film transistor array (not shown) formed in an active area 120 and a metal pattern 140 formed along one side of a periphery of the active area 120. In addition, a second alignment layer 151 is formed on a second substrate 150 having a color filter array (not shown) formed in the active area 120 and a black matrix 130 formed along the periphery of the active area 120.
In FIG. 4B, a thermo-hardening sealant 110 is formed along the periphery of the active area 120 on the first alignment layer 101, and spacers 102 are positioned on the second alignment layer 151. The thermo-hardening sealant 110 is formed of a narrow bead since a line width of a black matrix (not shown) formed along the periphery of the active area 120 of the first substrate 100 is relatively narrow.
In FIG. 4C, the first substrate 100 is aligned over the second substrate 150 so that a surface of the first substrate 100 on which the thermo-hardening sealant 110 is formed faces a lower direction. The first and second substrates 100 and 150 are then bonded to each other, and the thermo-hardening sealant 110 is hardened for one hour at 140° C. in a conventional hot press 170.
In FIG. 4D, after the bonded substrates have been cut into a plurality of individual unit panels, a liquid crystal material 103a is injected in each of the unit panels through an injection inlet 111 by a vacuum injection process. The liquid crystal injection is carried out by the vacuum injection process using a pressure difference between an interior of the unit panel and an ambient pressure of the processing chamber. The injection inlet for the liquid crystal material injection is sealed after completion of the liquid crystal injection process.
The thermo-hardening sealant is commonly selected from a group including of epoxy resin, urethane resin, and phenol resin. An epoxy ring of the epoxy resin is opened by a hardener such as amine or amide, and the opened epoxy ring becomes a reactive site so as to open another epoxy ring as a chain reaction, whereby a polymer chain is generated. This reaction is called “hardening.” A room-temperature-type hardening epoxy resin becomes active immediately at a room temperature, while a thermo-hardening type epoxy resin is hardened within 30˜60 minutes by being heated at 120˜140° C. In order to complete the above reaction, a heat application method is commonly used. A hardened epoxy compound enables sufficient bonding of the two substrates to each other, and the hardened epoxy compound has a relatively large density.
Unfortunately, the method of fabricating the liquid crystal display device according to the related art has disadvantages. First, as panel size increases, the liquid crystal material injection process is time consuming, whereby insufficient liquid crystal material injection may occur leading to failure of the device. Second, unhardened sealant may leak into the active area of the unit panel, thereby contaminating the liquid crystal material and causing stains.